Re: Extending a third party tagged type while adding finalization

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2017-12-03 16:10, AdaMagica wrote:
> Am Sonntag, 3. Dezember 2017 10:29:07 UTC+1 schrieb Dmitry A. Kazakov:
>>      type T is new Ada.Finalization.Controlled with record
>>         Self : not null access T'Class;
>>      end record;
>>      procedure Initialize (X : in out T);
>>      procedure Foo (X : in out T) is abstract;
>>
>>      type S is new T with ...
>>      overriding procedure Foo (X : in out S);
>>
>>      procedure Initialize (X : in out T) is
>>      begin
>>         X.Self.Foo; -- Boom!
>>      end Initialize;
> 
> Again an example of cryptic code I do not understand what it is
> aimed  at to demonstrate.

It demonstrates dispatch from Initialize (of T) to a procedure (Foo) of 
the derived type (S) before the derived type's Initialize is called.

> All I can see is that it is illegal Ada.

It is perfectly legal Ada. Initialize is not a constructor, it is just a 
primitive operation. So there is no promises made and no promises to 
fulfill regarding its semantics. One can call it anywhere, any number of 
times, in any order, everything is up to the unfortunate programmer.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de